1. Field of the Invention
This invention relates to methods of preparing fibrous products by extrusion of dopes into coagulating baths. More particularly, it relates to a method of preparing gradually stretched fibers from a single-cell dope extrudate which is exposed to a moving liquid coagulating bath of increasing velocity which causes the extrudate to gradually stretch.
2. Description of the Prior Art
The preparation of proteinaceous textured food products by spinneret extrusion into a coagulating bath is old in the art. The products so produced can be used as a partial substitute for meats since they generally have a protein content of about 50 percent or more.
One example of such a prior art process is described in U.S. Pat. No. 2,682,466 to Boyer. The filaments are generally produced by dispersing the protein starting material in a suitable dispersing medium such as an alkaline aqueous solution. The dispersion is then forced through a spinneret die and passes into a coagulating bath, which is generally an acid salt solution, causing the streamlets coming through the spinneret to be precipitated into the form of filaments. The resulting filaments are then stretched to provide the orientation and toughness required to simulate meat fibers. Stretching of the filaments was accomplished through the use of a take-up roll or a series of rolls rotating at increasing speeds.
A different approach to fiber formation is illustrated by U.S. Pat. No. 3,794,731 (1974) to Dannert et al. In this process, the protein fibers are prepared by extruding the alkaline protein solution through the die and intimately contacting the extrudate with a fast acting acid gas traveling at a velocity greater than the extrudate. The acid gas causes the proteins to coagulate to form fibers, and the speed and direction of the gas are such to cause a reduction in the diameter of the coagulating fibers due to a pulling action. The resulting fibers are then recovered by various means.
Another approach is illustrated by U.S. Pat. No. 3,889,010 (1975) to Brouwer. In this process the protein solution is foamed prior to extrusion such that the foam contains not more than 50 volume percent liquid. The foam is then extruded into the coagulating bath so that the relatively low density of the foam causes the extrudate to rise as the gas bubbles escape. This rising action consequently causes the extrudate to be stretched so long as the rate of extrusion is slower than the speed of the rising foamed extrudate. Additional stretching is obtained if the coagulating bath is recirculated such that the bath flows parallel to the path of the extrudate. The product is recovered by a take-up roll.
It has been found that the use of rollers such as are used in the various processes exemplified by the Boyer patent is often cumbersome and costly, particularly when applied to the texturization of protein materials. Also, the use of an acid gas as the coagulating agent as exemplified by the Dannert et al. patent can provide operational difficulties on a commercial scale due to the corrosive nature of the acid gas. In addition, a process of the type illustrated by the Brouwer patent is rate-limited by the speed at which the foamed extrudate will rise, and the composition of the extrudate is similarly limited by the necessity of having a sufficient gas content. And furthermore, neither of the two processes last mentioned provides a means for gradually stretching the extruded filaments by exposing them to a gradually increasing pulling force.
Therefore, it is an object of this invention to provide a method of gradually stretching a coagulable extrudate without the use of rollers or gaseous moving agents. This and other objects will become apparent upon further reading of this specification.